Fireproofing cellulose-containing materials

ABSTRACT

Cellulosic fiber-containing board products of improved fireretardant characteristics are obtained by treating the cellulosic fibers with urea prior to board formation and decomposing the urea in situ, for instance in the dewatered mat during board fabrication. Cellulosic fiber-containing boards having improved flame-spread ratings are obtained when the cellulosic fibers and urea are reacted at temperatures in excess of the decomposition temperature of urea, i.e., temperatures above about 380* F., but below the temperature at which the cellulosic fibers degrade. Preferably, the fibers are treated with aqueous urea solutions prior to board formation.

,1 ones Dec. 18, 1973 FIREPROOFING CELLULOSE-CONTAINING MATERIALS [75] Inventor: James R. Jones, Lancaster, Pa.

[73] Assignee: Armstrong Cork Company,

Lancaster, Pa.

[22] Filed: July 24, 1972 [21] Appl. No.: 274,327

[52] US. Cl 162/145, 8/195, 162/159 [51] llnt. Cl D2lh 3/00 [58] Field of Search 162/159, 158, 142, 162/145, 181 R, 171; 106/15 F, 15 P; 117/136; 8/195 [56] References Cited UNITED STATES PATENTS 2,278,285 3 1942 Reese 117/136 3,398,019 8/1968 Langguth... 3,042,578 7/l962 Penning 162/171 Primary ExaminerS. Leon Bashore Assistant Examiner-Peter Chin Attorney-William G. Taylor 5 7] ABSTRACT Cellulosic fiber-containing board products of improved fire-retardant characteristics are obtained by treating the cellulosic fibers with urea prior to board formation and decomposing the urea in situ, for instance in the dewatered mat during board fabrication. Cellulosic fiber-containing boards having improved flame-spread ratings are obtained when the cellulosic fibers and urea are reacted at temperatures in excess of the decomposition temperature of urea, i.e., temperatures above about 380 F., but below the temperature at which the cellulosic fibers degrade. Preferably, the fibers are treated with aqueous urea solutions prior to board formation.

7 Claims, No Drawings 1. Field of the Invention This invention relates broadly to the treatment of fibrous cellulosic-containing materials with urea to produce products of improved fire-retardant characteristics.

2. Description of the Prior Art The use of wood fiber insulation board and acoustical panels and mineral board products wherein fibrous newsprint is utilized as one of the chief board-forming fibrous ingredients has gained widespread acceptance in the building trades. The flammability of these products is a drawback in some applications since most building fires feed on cellulosic fuels and since the wood fiber and newsprint contribute to the flammability of products in which they comprise major constituents. It is known to make such board products contain-'- ing cellulosic fibrous materials fire-retardant by incorporating within the board products special fire retardants. For example, the use of certain ammonium salts including ammonium phosphates and ammonium borates are known to reduce the flammability of such cellulosic materials (See U. S. Pat. Nos. 3,398,019 and 3,629,055). In forming board products, it is also known that they should be dried at temperatures in excess of urea, the urea preferably being added as a solution which is slurried with the fibers prior to board formation. The urea is then reacted in situ at a temperature above the temperature at which urea decomposes generally above about 380 F. For ease of reaction we have found a temperature of about 390 F. to be practical. The maximum reaction temperature must be kept below the temperature at which the cellulosic fibers start degrading. When urea decomposes, theoretically among the decomposition products formed are isocyanic acid, biuret and it is also probable that some cyanthe decomposition temperature of the fire retardant 1 utilized. It is also known from U. S. Pat. No. 3,398,019 that certain undesirable color changes in cellulosic fibrous-containing board products can be minimized by incorporating a decomposition inhibitor in with the ammonium salt fire retardant. Urea is specifically mentioned as such an inhibitor.

SUMMARY OF THE INVENTION We have now found that cellulosic materials such as wood fibers and pulped newsprint may be rendered fire retardant by reaction with decomposition products of urea. Generally, a solution of urea is added to the pulped newsprint or wood fibers and the fibers reacted with urea at a temperature in excess of the temperature required to decompose urea, but below that at which the fibers degrade. On decomposition within the temperature range the decomposition products of urea react with the available hydroxyl radicals of the cellulosic fibers and form a product having much improved flame-retardant properties.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Most board products such asacoustical ceiling tile and panels contain cellulose fibers either in the form of pulped newsprint or pulped ground wood fiber. Since most building fires feed on cellulosic fuels, a great aduric acid is also formed. It is evidently some or all of these decomposition products which react with the available hydroxyl radicals in the cellulose molecule and thus render the cellulosic material incombustible. Thus, it is possible to render the cellulosic material incombustible by reacting the cellulose molecule directly with cyanuric acid and biuret, but it is preferable to initially utilize an aqueous solution of urea to treat the fibers and then to react the decomposition products of urea with the cellulose in situ at the elevated temperature required to decompose urea due to the economics and the important fact that urea is water-soluble and thus, in the case of wood fiberboard, can be readily utilized when slurrying of the fibers in the board formation process.

When cellulosic fibers and urea are reacted in situ at temperatures less than about 380 F., there is substantially no change in the flammability of the product. At reaction temperatures of about 380 F. and above, a

substantial reduction in the flammability of the treated vantage could be obtained if the cellulose-containing materials could be rendered incombustible or fireretardant at a nominal cost.

I have discovered that urea will react with cellulosecontaining materials such as boards containing newsprint and wood fiber to render the cellulosic fibrous material substantially incombustible. Board products formed containing the treated cellulosic fibrous materials have greatly reduced flame spreads.

In order to render the cellulose fibers flameretardant, it is necessary to react the fibers in situ with fibers is achieved.

Generally, we have found that the weight pick-up, by the fibers, of urea from solution during slurrying varies with the nature of the cellulosic fibers. In order to significantly reduce flammability, a weight ratio of urea to cellulosic fibers of 2.0 to 1.0 or greater is required with a weight ratio of urea to cellulosic fibers of greater than about 2.5 to 1.0 being preferred. To obtain a significant reduction in flammability of pulped newsprint, a concentration of about 50 percent by weight of urea in water solution is required whereas as low as 30 percent solutions of urea give significantly improved flameretardant properties when slurrying pulped wood fiber.

The boards may be readily formed from slurries using conventional board-forming equipment such as Olivers and Fourdriniers, it being preferred to pre-react the newsprint and urea prior to slurrying with conventional mineral board-forming compositions when forming the newsprint-containing mineral board products, whereas the slurry of wood fibers and binders such as starch in a water solution of urea can be used directly to form the water-laid web in the production of wood fiberboard products, the urea being reacted in situ with the fibers in the board during the drying cycle.

To determine the effectiveness of the newsprint fiher-urea reaction products, shredded newsprint was soaked for 30 minutes in urea solutions containing 40, 50 and 60 percent by weight of urea. After drying and after reaction at 200 C. for 1.5 hours in an oven, the treated newsprint was tested using a Bernz-O-Matic propane torch flame. The treated newsprint obtained utilizing the 40 percent urea solution supported combustion while the newsprint obtained from the 50 percent and 60 percent urea solution was completely incombustible.

The same type of experiment was conducted with wood fiber using a 50 percent urea solution, and the wood fiber resulting from this treatment was completely incombustible when placed into the flame of a Bernz-O-Matic propane torch.

A further test was made to evaluate the effectiveness of the urea reaction wth cotton cellulose. I-Iere cotton was soaked in a 50 percent urea solution, the excess solution squeezed from it, dried at 250 F. and reacted at 392 F. for 1.5 hours. Using the same propane torch test to test flammability, it was found that the flammability of the treated cotton cellulose was greatly reduced, although not completely incombustible like the treated newsprint or wood fiber. This can probably be explained in that wood cellulose is much more easily reacted than cotton cellulose due to the high degree of crystallinity present in the cotton cellulose and would appear to explain the lack of complete incombustibility of the treated cotton cellulose material.

To further evaluate the effectiveness of the use of the 50 percent urea solution, boards were prepared in duplicate using a control formulation containing:

Ingredients Percent by Weight Mineral Wool 56.85 Newsprint (untreated) 15.00 Perlite 20.12 Tapioca 7.68 Alum 0.31 Nalco 635 0.05

For the test formulation, boards were prepared from the following composition:

Nalco 635 The above formulations were dispersed in water as a 3 percent slurry from which 10 boards were prepared SAG Both sanded and painted and sanded uncoated boards (l foot X 2 feet) were placed in a sag room on a three-day cycle (24 hours at 82 F. and 80 percent R.l-I.; 30 hours at 82 F. and 86 percent R.I-I.; and 18 hours at 82 F. and 35 percent R.H.). The use of the urea-treated newsprint at the 25 percent level resulted in no significant detriment to the board sag when compared to the control board containing 15 percent untreated newsprint. There was slightly more sag in a urea-treated newsprint-containing board which was sanded and uncoated and slightly less sag in a ureatreated newsprint-containing board which was sanded and painted.

IGNITION LOSS Theoretical Theorectical Found Found Control Test Inorganic 77.32 67.32

MODULUS OF RUPTURE (psi) ganic 22.68 32.68

Inorganic Organic Control Test Correeled MOR 148.0 114.0

Lb. per Bd. Ft. 1.23 1.17

Actual MOR 206.5 143.0

Thickness 0.692 0.691

Break 19.8 13.8

Sample Control Test Although the modulus of rupture for the board prepared from the newsprint reacted with urea was lower than the control which utilized untreated newsprint at a lower level, the corrected MOR was more than sufficient for a structurally adequate board product.

On eight runs, the control panels gave flame spread ratings varying from 16 to 32 with an average flame spread rating of 22.0. For the test material, the flame spread ratings for five runs varied from 1 1 to 16, with an average flame spread rating of 13.8. I

25-FOOT TUNNEL TEST A.S.T.M.-E84) Samples of the control and of the test material containing the 25 percent treated newsprint were tested using a sample size of 21 X 25.

7-l'oot Burn Time 4 min.

7 min.

25-foot Flame FSR l0 Sample Control Test While, under the conditions of this test, both boards calculated out to a flame spread resistance of 10, the superiority of the treated newsprint-containing board is readily apparent when the time for the actual flame spread is compared.

Two formulations similar to the above board formulations were utilized except in this instance boards of the test material were prepared in which all of the in-' gredients for the test boards were added to a 50 percent urea solution so that the total board formulation was intimately mixed with the urea solution. Sheets prepared from the control formulation were dried at 300 F. while those prepared from the test formulation were placed in a 200 C. (392 F.) oven in order that the reaction between the urea decomposition products and the hydroxyl groups in the cellulosic fibers would occur within the prepared sheet. The boards thus prepared have the following properties:

Lbs. I

per bd. ft.

Corrected MOR Actual Found 21.5 60.9

Theoretical 22.68 62.68

Control Test Even though the test formulation contains a large percentage of what is termed organic," the flame spread resistance is essentially identical to the control. The one detrimental effect resulting from this test formulation technique is that it produced a board of high density. Thus, while this approach has utility in a board prepared from wood fibers and starch binder, for a mineral-containing fiberboard it appears that the newsprint and urea should first be reacted and then the treated newsprint added at the 25 percent level to the mineral-board formulation.

Several boards were prepared from a slurry of 144.75 pounds of refiner ground wood (pine) and 5.25 pounds of wheat clears slurried in 6,000 pounds of a 36 percent urea solution. The boards prepared had an average density of 1.47 pounds per board foot with an average break of greater than pounds, an average MOR of greater than 310, an average FSR (30/30) of 61 an av erage thickness after pressing of between 0.675 and 0.725 and an average thickness after drying of between 0.650 and 0.700. The average total sag was 100 mils or less with the average ignition loss being 89 percent. The 30/30 flame spread resistance of 61 compared very favorably with the 30/30 flame spread rating of 128 for a control board formed of the same ingredients which were not slurried with the urea solution.

Another pilot plant run was conducted in which 193 pounds of refiner ground wood (pine), 7 pounds of wheat clears and just enough alum to adjust the pH of the slurry to a pH of 6.0 to 6.5 was slurried in 6,000 pounds of a 50 percent urea solution. From this slurry, using a conventional Oliver, a total of 26 boards were prepared. The urea-cellulose reaction was conducted by passing the wet board, after formation, through drying ovens set at a temperature in the range of 425 F. to 450 F. with a total of four complete passes being required to achieve dryness plus reaction. For the control, a standard wood fiber board was used formed from the same ingredients in the same proportions but slurried in water and all boards, both control and test, were face sanded to 550 mils and uncoated.

The following data was obtained on the board products prepared above:

30/30 Tunnel Test FSR Control 130 Treated 45 MOR Density Break MOR pbf lbs (psi) Control MD 1.34 26.5 433 AMD 1.37 20.5 339 Treated MD t.33- 19.5 316 AMD 1.30 15.0 272 NBS Smoke v r a Trans. DM DM (Corn) Control 2.60 209 0/209 Treated 4.95 172 0/l72 Sag (l- X 2 board) Initial 80% 80% 86% 35% 35% Tues. Wed. Thurs. Fri. Tues. 9 AM 4 PM 9 AM 3 PM 9 AM Control 30 --47 65 -95 l73 Treated 0 -54 -68 -88 67 Overall 'Iotal Sag: Control l43 Treated -67 -Foot Tunnel Test Treated Board:

Fuel Contribution 29.6 Smoke developed l6.l Maximum flame spread of 12 ft. No flaming when exposure out.

'Method for Measuring Smoke from Burning Materials" by D. Gross, et al.; A.S.T.M. Special Technical Publication No. 422 (1967) These results establish that the wood fiberboard prepared from a slurry treated with urea and then reacted with the urea in situ after board formation possesses a superior flame spread resistance and lower smoke values as well as improved sag when compared to an untreated board. All other properties are essentially unaffected by the treatment.

What is claimed isz 1. The method of reducing the flammability of cellulosic fibers which comprises treating the fibers with an aqueous solution of urea to provide a dry weight pickup of urea by the fibers of greater than about 2.0 parts by weight urea to 1.0 parts by weight fiber and reacting the fibers and urea in situ at a temperature (above that at which the urea decomposes, the weight ratio, on a dry weight basis, of urea to cellulosic fibers being about 2.0 to 1.0 or greater) greater than about 380 F. but less than that at which the fibers degrade for a period of time sufficient to improve the fire-retardant characteristics of the cellulosic fibers.

2. The method in accordance with claim 1 in which the cellulosic fibers are pulped newsprint, and the weight ratio of the urea to newsprint fibers is about 2.5 to 1.0 or greater.

3. The method in accordance with claim 1 in which the cellulosic fibers are pulped wood fibers, and the weight ratio of the urea to wood fibers is about 2.5 to 1.0 or greater.

4. A method of manufacturing afire-retardant woodfiberboard product comprising:

forming a slurry of wood fiber and starch binder in a water solution of urea of a concentration such as to provide a pick-up of urea to wood fiber of greater than about 2.0 parts by weight of urea to 1.0 parts by weight wood fiber (or greater), on a dry weight basis;

forming a wet-laid mat from said slurry on a boardforming machine; and

drying the mat and reacting the urea with the wood fiber by heating the dried mat to a temperature above about 380 F. but below the temperature at which the wood fiber degrades for a period of time sufficient to decompose the urea and to react the decomposition products with the available hydroxyl radicals in the cellulosic wood fiber and thus improve the fire-retardant characteristics of the board.

5. The method in accordance with claim 4 in which the weight ratio of the urea to wood fibers is greater than about 2.5 to 1.0. 1

6. A method of manufacturing a mineral fiber board product containing pulped'newsprint comprising:

slurrying the pulped newsprint with a water solution of urea of a concentration sufiicient to provide a pick-up of urea to newsprint of greater than about 2.0 parts by weight urea to 1.0 parts by weight newsprint (or greater), on a dry weight basis; drying and reacting the treated newsprint by heating the treated newsprint to a temperature (above) greater than about 380 F. but below the temperaforming a wet-laid mat from the slurry on a boardforming machine and drying the mat to form the mineral fiber board product.

7. The method in accordance with claim 6 in which the weight ratio of the urea to newsprint fibers is greater than about 2.5 to 1.0. 

2. The method in accordance with claim 1 in which the cellulosic fibers are pulped newsprint, and the weight ratio of the urea to newsprint fibers is about 2.5 to 1.0 or greater.
 3. The method in accordance with claim 1 in which the cellulosic fibers are pulped wood fibers, and the weight ratio of the urea to wood fibers is about 2.5 to 1.0 or greater.
 4. A method of manufacturing a fire-retardant wood-fiberboard product comprising: forming a slurry of wood fiber and starch binder in a water solution of urea of a concentration such as to provide a pick-up of urea to wood fiber of greater than about 2.0 parts by weight of urea to 1.0 parts by weight wood fiber (or greater), on a dry weight basis; forming a wet-laid mat from said slurry on a board-forming machine; and drying the mat and reacting the urea with the wood fiber by heating the dried mat to a temperature above about 380* F. but below the temperature at which the wood fiber degrades for a period of time sufficient to decompose the urea and to react the decomposition products with the available hydroxyl radicals in the Cellulosic wood fiber and thus improve the fire-retardant characteristics of the board.
 5. The method in accordance with claim 4 in which the weight ratio of the urea to wood fibers is greater than about 2.5 to 1.0.
 6. A method of manufacturing a mineral fiber board product containing pulped newsprint comprising: slurrying the pulped newsprint with a water solution of urea of a concentration sufficient to provide a pick-up of urea to newsprint of greater than about 2.0 parts by weight urea to 1.0 parts by weight newsprint (or greater), on a dry weight basis; drying and reacting the treated newsprint by heating the treated newsprint to a temperature (above) greater than about 380* F. but below the temperature at which the newsprint degrades for a period of time sufficient to decompose the urea and react the decomposition products with the available hydroxyl radicals in the newsprint and thus improve the fire-retardant characteristics of the fibers; slurrying the thus-treated newsprint in a water solution containing the remaining mineral board-forming ingredients; and forming a wet-laid mat from the slurry on a board-forming machine and drying the mat to form the mineral fiber board product.
 7. The method in accordance with claim 6 in which the weight ratio of the urea to newsprint fibers is greater than about 2.5 to 1.0. 